Clostridium difficile (C. difficile) is a gram-positive anaerobic bacillus and is the causal agent of antibiotic-associated pseudomembranous colitis in humans and other mammals. Antibiotic associated pseudomembranous colitis results from the use of broad-spectrum antibiotic agents such as clindamycin that have been administered to treat a primary bacterial infection. The antibiotic therapy often leads to the destruction of endogenous intestinal flora which allows for the colonization of C. difficile in the gut leading to the observed diarrhea in about 10% of treated patients and pseudomembranous colitis in about 1% of treated patients. C. difficile causes antibiotic associated diarrhea and almost all cases of pseudomembranous colitis.
The colitis of Clostridium difficile-associated disease results from the synergistic action of C. difficile toxin A and toxin B upon the colon mucosa (Barroso et al., 1990; Dove et al., 1990; Lyerly et al., 1988). Together, the toxins disrupt cell-cell tight junctions of the colon thereby allowing the bacterium to adhere to the underlying colon tissue and feed upon the nutrients released by the damaged epithelium (Borriello, 1998). Successive rounds of C. difficile colonization, replication, and toxin production lead to a vigorous host inflammatory response resulting in further degradation of the gut tissue, the pseudomembranous pathology associated with the diarrhea and the pain observed in Clostridium difficile-associated disease.
Most patients with C. difficile associated disease are treated effectively with vancomycin or metronidazole. Non-antibiotic treatment modalities that have been investigated include tolevamer, a toxin binding polymer (Louie et al., 2006), and an antiparasitic medication, nitazoxanide (Bartlett, 2006). However, relapses occur in about 20-25% of patients. Therefore, there is still a need for additional effective treatments of Clostridium difficile associated disease in humans.
Immunological treatment is valuable because vaccination against toxins A and B stimulates active immunity against C. difficile disease in animals (Libby et al., 1982). However, vaccines against the organism and its toxins are not available for human use.
Passive immunization is another immunological treatment. Studies indicate that such passive immunization provides protection (Boesman-Finkelstein et al., 1989; Brussow et al., 1987; Fayer et al., 1990; Hilpert et al., 1987; Mietens et al., 1979; Tacket et al., 1988; Yoshiyama and Brown, 1987). Serum antibodies against C. difficile protect hamsters against C. difficile disease after oral administration. Passive immunization with bovine antibodies has been proposed as a treatment for other infectious diseases of the gastrointestinal tract, such as diseases caused by rotavirus, enteropathogenic and enterotoxigenic Escherichia coli, Vibrio cholerae, and Cryptosporidium parvum. It has been reported that bovine immunoglobulin G (IgG) concentrate from the colostrum of cows vaccinated with C. difficile toxoid protects hamsters against antibiotic associated cecitis. The hamsters were protected when treated before the onset of diarrhea but not after diarrhea began (Lyerly et al., 1991). IgG directed against toxins A and B of C. difficile are present in the general population (Bacon and Fekety, 1994). Human intravenous immunoglobulin derived from plasma donors has facilitated treatment in some patients, especially patients who lack circulating antibodies to the C. difficile toxins (Cone et al., 2006; Leung et al., 1991; McPherson et al., 2006; Salcedo et al., 1997; Wilcox, 2004).
In vitro experiments have demonstrated that polymeric immunoglobulins are superior to monomeric immunoglobulin in preventing C. difficile toxin damage to intestinal epithelial cell monolayers (Stubbe et al., 2000). Selective neutralization of C. difficile toxin by serum IgA has also been demonstrated (Johnson et al., 1995). Administration of an immunoglobulin product containing specific antibodies to C. difficile results in the elimination of C. difficile toxins and also killing of the bacteria within the colon as detailed in U.S. Pat. No. 5,773,000. Such passive immunization therefore provides an effective approach for the treatment of C. difficile associated diseases such as colitis, pseudomembranous colitis and antibiotic associated diarrhea. This is especially important for patients experiencing multiple relapses.
Current treatments for C. difficile associated disease use antibiotics such as metronidazole and vancomycin. These drugs result in further disruption of the intestinal flora and are associated with a 20-25% incidence of disease relapse.
As reported by Tjellstrom, monomeric polyclonal IgA admixed with polyclonal IgG (2:1) derived from plasma (IgAbulin, Immuno, Vienna) (100 mg/mL) when administered orally 3 times daily in 4 mL doses for 3 weeks to a three and one-half year old child with antibiotic-associated diarrhea and C. difficile toxin A in his stools with concurrent vancomycin administration caused improvement (Tjellstrom et al., 1993). Polyclonal IgG derived from pooled plasma was administered to a second child with refractory C. difficile diarrhea who had failed treatment with antibiotics and intravenous polyclonal IgG. This patient received oral polyclonal IgG at 200mg/kg/day every 2 days for 3 doses together with courses of oral vancomycin and Lactobacillus. The child had recovered at follow-up evaluation 2 weeks later (Saturna at al. 2006). These reports demonstrate the efficacy of oral passive immunization with pooled immunoglobulins derived from the general population. It appears that monomeric circulatory immunoglobulins possess efficacy. However, increased efficacy is achieved by dimeric secretory IgA and pentameric secretory IgM owing to the propensity of monomeric circulatory immunoglobulins to degrade in the gastrointestinal tract. The dosing requirements of monomeric immunoglobulins therefore increase treatment costs. The prior art use of circulatory immunoglobulins failed to explore antigen specific secretory IgA and IgM as a potential medicament.
It is recognized that the large majority of the total IgA fraction is not specific for toxins A or B. As a result, this major fraction may be of little clinical value for the treatment of C. difficileassociated disease. Therefore, further chemical refinement of this bulk material may be uneconomical in terms of reagent costs and effort. In addition, higher toxin binding titers are achieved with isolated C. difficile antitoxin-specific IgA, as compared to bulk IgA.
Thus, there exists a need for an antigen specific IgA and IgM therapeutic that is resistant to gastrointestinal tract degradation. There also exists a need to provide such a therapeutic in a dosing form well suited for treating an infected subject.